SW20 aero theory. (56k = if u patient)

[Perky]

This would be an excellent experiment.

I think that you would have to measure air pressure directly rather than inferring it from air speed. I assume that the inverse relationship between air speed and pressure only holds for a given mass of air, otherwise falling objects (or accelerating cars) would face decreasing air resistance -- and eventually none; instead of which they reach a terminal velocity limited by air resistance.

[Perky]

Also I have been thinking about why mods like this arent very common.... Because what other car could you do this to? most cars have an engine in the way.

Many contributors here have plans to remove their engines to swap or repair them. Perhaps while the engines are out they could do some speed trials on these bonnet modifications.

[fivebob]

I just happen to have the devces you need to do this job

[Mr Revhead]

cunning, very cunning...

how sensitive is the pressure sensing of the motec?
and a real time read out on the dash... nice. would you use the boost function, or is there another function on them that does it?

iv always wantd to do some proper aerodynamic experiments...

[fivebob]

cunning, very cunning...

how sensitive is the pressure sensing of the motec?

Very sensitive it was designed for doing on car aero measurement has a range of -60" -> +60" of water with 0.01" resolution

and a real time read out on the dash... nice. would you use the boost function, or is there another function on them that does it?

The dash display is Ok, but the real power of the ADL is is it's logging and decision making capabilities. The ADL is fully user programmable to display whatever data you want on the dash and has multiple modes that the driver can select. One illustration of the power of the unit was that a Driver was complaining that he was running out of brakes at the end on Conrod Straight, after looking at the logged data the engineers determined that the driver was leaving his foot on the accelator when braking, so they told hime they'd fixed the problem and sent hime back out, next time he came in he said it's still doing it and asked the engineers why the dash said "You are a f..kwit" and they kindly explained the error of his ways.

iv always wantd to do some proper aerodynamic experiments...

I'm just wating for desktop CFD to become affordable

[Mr Revhead]

haha nice one.

im a complete n00b when it comes to electrics and ecu's.... is that aero measument a standard feature? or an add on that works with the ecu and dash?.... i think its time i looked more into these motecs....

[Perky]

fivebob,

can that thingy measure eight points at once? That looks like a pretty powerful tool for this kind of experiment.

[RomanV]

Hmmm, the fun you could have with that Motec unit.
Yes, is that eight inputs? That looks awesome.

However, since the budget for any aerodynamic experiments I do is non-existant, I think a tool such as that would be out of my price range.

However, I was thinking of a much more crude system. I wouldnt need datalogging, as all comparisons would be made at similar speed intervals. (maybe at 80kph, 100kph, 120kph) On closed roads of course. *cough*

I could have a passenger reading the outputs and writing them down at various speeds.

I was thinking it would be possible to use an old MAP sensor (or five) to ascertain the pressure at various points.

I mean would that be possible? It wouldnt be hugely accurate, but it wouldnt need to be. If the difference is miniscule, then it doesnt concern me anyway.

I only have a basic understanding of how a MAP sensor works however.
I would imagine that it is basically a variable resistor of sorts? Does it output a variable current/voltage based on the pressure that it senses? Thats my assumption of how it would work anyway.

Some wind tunnel simulation software would be heaps of fun to play with!

[fivebob]

is that aero measument a standard feature? or an add on that works with the ecu and dash.

The sensor is an add-on and you simply configure the dash to calibrate the voltage output to a pressure reading.

Don't think it would work with the ECU very well though as it doesn't really have enough spare outputs or the capacity to convert the units so you could only log voltage and use the interpreter to convert that. Also the dash samples at 1000/sec the ECU is on 200/sec so the dash is much better suited to aero measurements.

i think its time i looked more into these motecs....

Unfortunately the dash an aero sensors are way beyond most peoples budgets, although the prices have dropped recently you're still looking at more than $10,000 to do the job

[Mr Revhead]

so reading is all ill be doing then.....

cheers for that, really is time i learnt more about this sort of thing

[fivebob]

Hmmm, the fun you could have with that Motec unit.
Yes, is that eight inputs? That looks awesome.

Yes eight inputs, I have two of them so I can do 16

However, since the budget for any aerodynamic experiments I do is non-existant, I think a tool such as that would be out of my price range.

Yes, out of most Toyspeeders price range I'm afraid, but thats the cost of quality data.

I was thinking it would be possible to use an old MAP sensor (or five) to ascertain the pressure at various points.

I mean would that be possible? It wouldnt be hugely accurate, but it wouldnt need to be. If the difference is miniscule, then it doesnt concern me anyway.

They wouldn't be accurate enough, by my approx calculations each kg of downforce requires only 0.001psi , even if my calculation were out by a factor of 10 I doubt you would be able to see the differences in the changes you propose.

You could try the el cheapo method of coloured water in vacuum tubes, though they'd need to be pretty tall and you still have to have a way of recording the data (passenger/video). I used to have a set of tubes to tune 4 cylinder motorcycle carbs, they used mercury (shudder) but for this case water would be better. There are bound to plans around for building them somewhere on the net.

Some wind tunnel simulation software would be heaps of fun to play with!

Got a spare $20k? http://www.cham.co.uk

[RomanV]

Well there goes that Idea then. Infact pretty much all of my ideas.

I suppose it isnt really even worth attempting, if I cant verify the results. It would be stupid to do all of that work, and then end up magnifying the effect, rather than reducing it.

Thanks for the input Fivebob! Appreciated.

*goes back to drawing board*

[Mr Revhead]

did i miss something? why are you giving up??

[RomanV]

Well using MAP sensors wouldnt work, for the reasons Fivebob outlined. 10k for a proper set of sensors, or 20k for a wind tunnel simulator is out of my price range.

I understand the concept of the water tube testing, but I dont think it would be practical.

So I havent given up, Im just out of ideas for the moment.

[Mr Revhead]

i reckon try the water test... wont cost much, so wont matter if it fails....

[fivebob]

Can't see any reason to give up, like I said the coloured water in tubes will be good enough to measure the results. Do a search on water manometers and you see what I mean, there's even some commercially available products like http://www.tq.com/product/index.asp?pid=af10a

[RomanV]

EDIT: I wrote this before I saw fivebobs post above.

The goal of this experiment would be to prove whether or not hood-vented radiator air would reduce frontal lift to any degree in an SW20.
If there is no practical way of verifying the results, then there is no point in attempting it.
Because it may have unforseen negative consequences, eg. More frontal lift being generated than before.
I may further investigate the water tube idea however. It just seems a bit clumsier than measuring electronically.

[fivebob]

Well using MAP sensors wouldnt work, for the reasons Fivebob outlined. 10k for a proper set of sensors, or 20k for a wind tunnel simulator is out of my price range.

The sensors are only 2k, and there are cheaper ways to log then, but still past your price range I guess.

I understand the concept of the water tube testing, but I dont think it would be practical.

Should be practical, just depends on the pressures, the lower the pressure the taller the manomenter you require but I don't think the pressures on the underside will be that low. Certainly less than in a airbox that I seen tested which required a 1.2m tube.

Besides which I might be persuaded to use my ADL & sensors if someone else is prepared to put the effort into doing the testing.

[blitza]

haha, manometer!hrmm, is really interesting doing the manometer test, and videoing the results, helps to have a spedo in the screen as well, think apexi R/SM. coloured water, plenty of tube, and some way of getting a static pressure to reference it all to.(you may need to make up a manifold to do this, kinda a average of all inputs, interior,left/rightside,boot,bonnet)
More importantly thou, what is yor intent with all that gear 5bob?

[RomanV]

I wont be starting this for quite some time yet.
I still have an engine swap project to start/complete first. (Or I might be able to slot this in there somewhere. )
It seems that there is a lot of speculation about mods like this, but no confirmed results anywhere. It would be awesome to be able to establish some facts. Especially so with a proper set of sensors.
Even some manometer based results would be satisfying, if they showed an improvement or otherwise.